A brass box with all the seams soldered should do the job. __________________________________________ David C Brown 43 Bings Road Whaley Bridge High Peak Phone: 01663 733236 Derbyshire eMail: dcb.home@gmail.com SK23 7ND web: www.bings-knowle.co.uk/dcb *Sent from my etch-a-sketch* On 9 July 2018 at 16:50, Sean Breheny wrote: > My understanding is that these newer fobs that are "touchless" use two > different frequency bands - one the traditional UHF and the other in the = LF > or VLF range. The LF one is used to determine proximity (being near field > only it is easier to deduce distance from signal strength). The UHF one i= s > used to transmit data or perform any functions which are intended to be > performed at a distance. > > I would suspect that aluminum foil is not going to attenuate LF or VLF > tremendously because the thickness is only on the same order as the skin > depth, not many skin depths. > > I also suspect that aluminum foil would have to be carefully arranged to > reliably block UHF since even a rather circuitous path out from the insid= e, > as long as it is wide enough, will allow signal transmission. > > I highly doubt that a conductive ESD bag is going to make much difference > to the signal strength. > > Most food cans (and other types of "tins") have coatings on them to prote= ct > the metal from corrosion and their lid does not make electrical contact > with the body of the tin when they are mated. Once again, this will permi= t > both LF and UHF transmission quite well. > > To be reasonably sure that you have placed your fob in an effective shiel= d, > even for UHF, would require that you use a container where the ENTIRE > perimeter of the lid makes good electrical contact with the body of the > container, with no more than a 2 or 3 millimeters gap between points of > electrical contact. > > It is a very educational exercise to attempt to completely shield an RX o= r > TX at UHF frequencies. It is actually quite difficult to do it. > > Sean > > > On Mon, Jul 9, 2018 at 11:25 AM, Denny Esterline > wrote: > > > > > > > > > > It seems to me the only way the key fob is going to be able to be > > > copied is if someone presses one of the > > > buttons to transmit the signal. If it is just sitting on a table or > > > hanging on a wall hook, how would > > > someone outside the home (or bldg.) cause the key fob to transmit? > > > > > > > > > > This is a misunderstanding. I cannot claim to know the underlying > > technology, but > > many new car keyfobs today are "proximity devices". Fob in pocket, pres= s > > button > > on dash to start car. Definitely do not have to press any buttons on th= e > > fob. > > > > I've not read Russell's linked article, but I did recently read an > article > > claiming > > thieves were using SDR as a repeater to significantly boost the range o= f > > what the > > car considers "proximity". The claim was with your keys on a hook by yo= ur > > front > > door, they could use a repeater outside and drive the car away. > > > > The really fun trick here is they make no effort to capture or crack an= y > > codes, > > just boost a signal. > > > > > > -Denny > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .